Background
Actinomycosis is a subacute-to-chronic bacterial infection caused by filamentous, gram-positive, non–acid-fast, anaerobic-to-microaerophilic bacteria. It is characterized by contiguous spread, suppurative and granulomatous inflammation, and formation of multiple abscesses and sinus tracts that may discharge sulfur granules. The most common clinical forms of actinomycosis are cervicofacial (ie, lumpy jaw), thoracic, and abdominal. In women, pelvic actinomycosis is possible.
For additional information on actinomycosis, see the articles Actinomycosis (dermatology focus), Actinomycosis (pediatrics focus), and Actinomycosis (ophthalmology focus).
Pathophysiology
Actinomycetes are prominent among the normal flora of the oral cavity but less prominent in the lower gastrointestinal tract and female genital tract. Because these microorganisms are not virulent, they require a break in the integrity of the mucous membranes and the presence of devitalized tissue to invade deeper body structures and to cause human illness.
Furthermore, actinomycosis is generally a polymicrobial infection, with isolates numbering as many as 5-10 bacterial species. Establishment of human infection may require the presence of such companion bacteria, which participate in the production of infection by elaborating a toxin or enzyme or by inhibiting host defenses. These companion bacteria appear to act as copathogens that enhance the relatively low invasiveness of actinomycetes. Specifically, they may be responsible for the early manifestations of actinomycosis and for treatment failures.
Once infection is established, the host mounts an intense inflammatory response (ie, suppurative, granulomatous), and fibrosis may then follow. Infection typically spreads contiguously, frequently ignoring tissue planes and invading surrounding tissues or organs. Ultimately, the infection produces draining sinus tracts. Hematogenous dissemination to distant organs may occur in any stage of actinomycosis, whereas lymphatic dissemination is unusual.
Cervicofacial actinomycosis
Cervicofacial actinomycosis is the most common type of the infection, comprising 50-70% of reported cases. This infection typically occurs following oral surgery or in patients with poor dental hygiene. Cervicofacial actinomycosis is characterized in the initial stages by soft-tissue swelling of the perimandibular area. Direct spread into the adjacent tissues occurs over time, along with development of fistulas (sinus tracts) that discharge purulent material containing granules with a yellow sulfurlike appearance (termed sulfur granules). Invasion of the cranium or the bloodstream may occur if the disease is left untreated.
Thoracic actinomycosis
Thoracic actinomycosis accounts for 15-20% of cases. Aspiration of oropharyngeal secretions containing actinomycetes is the usual mechanism of infection. Occasionally, thoracic actinomycosis results from the introduction of organisms via esophageal perforation, by direct spread from an actinomycotic process of the neck or abdomen, or via hematogenous spread from a distant lesion. Thoracic actinomycosis commonly presents as a pulmonary infiltrate or mass, which, if left untreated, can spread to involve the pleura, pericardium, and chest wall, ultimately leading to the formation of sinuses that discharge sulfur granules.
Actinomycosis of the abdomen and pelvis
Actinomycosis of the abdomen and pelvis accounts for 10-20% of reported cases. Typically, these patients have a history of recent or remote bowel surgery (eg, perforated acute appendicitis, perforated colonic diverticulitis following trauma to the abdomen) or ingestion of foreign bodies (eg, chicken or fish bones), during which actinomycetes are introduced into the deep tissues. The ileocecal region is involved most frequently, and the disease typically presents as a slowly growing tumor. Diagnosis is usually established postoperatively, following exploratory laparotomy for a suspected malignancy. Involvement of any abdominal organ, including the abdominal wall, can occur by direct spread, with eventual formation of draining sinuses. Pelvic actinomycosis most commonly ascends from the uterus in association with intrauterine contraceptive devices (IUCDs). In such cases, an IUCD has been in place for an average of 8 years.
Epidemiology
Frequency
United States
Actinomycosis is rare. During the 1970s, the reported annual incidence of actinomycosis in the Cleveland area was 1 case per 300,000 persons. Improved dental hygiene and widespread use of antibiotics for various infections have probably contributed to the declining incidence of this disease.
International
Actinomycosis occurs worldwide, with likely higher prevalence rates in areas with low socioeconomic status and poor dental hygiene.
Mortality/Morbidity
The availability of antibiotics has greatly improved the prognosis of all forms of actinomycosis. At present, cure rates are high, and neither deformity nor death is common.
Race
Actinomycosis has no racial predilection.
Sex
For unknown reasons, actinomycosis is more common in men than in women (male-to-female ratio, 3:1), with the exception of pelvic actinomycosis.
Age
Actinomycosis can affect people of all ages, but most cases are reported in young to middle-aged adults (aged 20-50 y).
Prognosis
When actinomycosis is diagnosed early and treated with appropriate antibiotic therapy, the prognosis is excellent.
The more advanced and complicated actinomycotic forms require aggressive antibiotic and surgical therapy for optimal outcome; however, deaths can occur despite such therapy.
Patient Education
Because actinomycosis is an endogenous infection, no risk of person-to-person transmission exists.
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Actinomycosis in the endometrial tissue, low-power view. Image courtesy of Paul Gibbs, MD.
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Actinomycosis in the endometrial tissue, high-power view. Image courtesy of Paul Gibbs, MD.
